Attribute monitoring in a class

[Joel Andres Granados]

Bruno Desthuilliers wrote:
> Joel Andres Granados a écrit :
>   
>> Hi list:
>>
>> I have googled quite a bit on this matter and I can't seem to find what 
>> I need (I think Im just looking where I'm not suppose to :).  I'm 
>> working with code that is not of my authorship and there is a class 
>> attribute that is changes by directly referencing it (object.attr = 
>> value) instead of using a getter/setter (object.setAttr(Value) ) 
>>     
>
> Which is the right thing to do in Python (I mean : *not* using 
> Java-style getters/setters).
>
>   
>> function.  The thing is that I have no idea when the change occurs and I 
>> would REALLY like to find out.
>> So here comes my question .....
>> Is there a function construct inside a python class that is 
>> automatically called when an attr is changed????
>>     
>
> yes : object.__setattr__(self, name, value)
>
> # example:
> class Class(object):
>     def __init__();
>        self.attr = "whatever"
>
>     def __setattr__(self, name, value):
>        object.__setattr__(self, name, value)
>        if name == 'attr':
>            print "It has changed"
>            # you can also print the call frame,
>            # or set a 'hard' breakpoint here...
>
> obj = Class()
> obj.attr = "other whatever"
>
> *Output:*
> It has changed
>
>   

I used this ^^^^^^^^^^^^^^^ one.  Thank for the help.
Works like a charm.
Regards

> Or you might turn attr into a property:
>
> class Class(object):
>     def __init__();
>        self.attr = "whatever"
>
>     @apply
>     def attr():
>         def fset(self, value):
>             self._attr = value
>             print "It has changed"
>         def fget(self):
>             return self._attr
>         return property(**locals())
>
> But unless you have other needs than simple tracing/debugging, it's 
> probably overkill.
>
> HTH
>